Iron oxides with a higher degree of refining

ABSTRACT

Iron oxides are upgraded by calcining at from 700 to 1200° C.

DESCRIPTION

[0001] The present invention relates to a process for upgrading ironoxide, which comprises calcining iron oxide at not less than 700° C.

[0002] EP-A-1 027 928 describes a catalyst, especially fordehydrogenation of ethylbenzene to styrene, which is prepared using aniron oxide obtained by spray roasting an iron salt solution, especiallyhydrochloric acid iron solutions (Ruthner process). The disadvantage ofsuch iron oxides is their high residual chloride content.

[0003] EP-A-797 481 discloses iron oxides as a starting material forcatalysts, especially for dehydrogenation of ethylbenzene to styrene,which are restructured by mixing with a further metal compound andsubsequent calcination and which have very small BET surface areas. Thedisadvantage of such a restructuring is the contamination of the ironoxide by the metal compound added.

[0004] JP-A-61-72601 discloses a fluidized bed process for crackingheavy hydrocarbons into lighter hydrocarbons using a pulverulentcatalyst prepared by slurrying up an iron oxide powder with water,.spray drying and finally calcining at temperatures between 1200 and1600° C. Disadvantages of this process are the immense cost andinconvenience and the high calcination temperatures.

[0005] EP-A-827 488 describes a process for reducing the residualchloride content in iron oxides, especially in iron oxides generated byspray roasting hydrochloric acid pickling wastes, by mixing the ironoxide with a hydrated metal compound and subsequent calcination. Thedisadvantage of this process is its cost and inconvenience.

[0006] U.S. Pat. No. 4,134,858 discloses roasting iron oxide at 800° C.before using it to prepare styrene catalysts. However, any residualchloride content in the iron oxide cannot be sufficiently lowered bythis method.

[0007] U.S. Pat. No. 2,414,585 discloses precalcining iron oxide forpreparing dehydrogenation catalysts. The iron oxide obtained is said tohave a BET surface area of <8 m²/g and preferably of about 4 m²/g. Suchcatalysts leave a lot to be desired.

[0008] It is an object of the present invention to remedy theaforementioned disadvantages.

[0009] We have found that this object is achieved by a novel andimproved process for upgrading iron oxide, which comprises calciningiron oxides at from 700 to 2500° C. The invention further provides noveliron oxides and their use as catalysts, and for the preparation ofcatalysts, especially for the preparation of catalysts fordehydrogenation of ethylbenzene to styrene.

[0010] The process of the invention can be carried out as follows:

[0011] The upgrading of the present invention may be applied to any ironoxide, but is preferably applied to iron oxides generated by working uphydrochloric acid waste liquids from steel pickling, for example,especially iron oxides generated by spray roasting hydrochloric acidpickling wastes (Ruthner process).

[0012] The iron oxide may be subjected to a batch operated or preferablycontinuous calcination at from 700 to 1200° C., preferably at from 840to 1150° C., particularly preferably at from 850 to 1100° C., especiallyat from 860 to 1000° C., or generally from 0.1 to 24 h, preferably from0.25 to 10 h, particularly preferably from 0.3 to 5 h, especially from0.5 to 1.5 h, without pretreatment, i.e., for example without mechanicalpretreatment, and preferably dry, i.e., without prior treatment withwater, an acid or base or some other material. Useful calcinationapparatus includes all known ovens. The calcination can be carried outbatchwise, for example in muffle furnaces, or continuously, for examplein rotary tube ovens or in belt calciners. Preference is given tocontinuous processes. The calcination can be carried out at just onetemperature or in stages at various temperatures or in the form of acontinuous temperature ramp. When the calcination is carried out inrotary tubes, the rotary tube should be equipped with tappers whichprevent sticking of the iron oxide to the wall of the rotary tube andensure continuous transportation of the iron oxide. Advantageously, thecalcination is carried out in smooth rotary tubes without internalfitments, and the residence time can be adjusted via the speed ofrotation, the feed speed and the inclination of the rotary tube. Thecalcination is further advantageously carried out under a gas stream,for example nitrogen or air, in order that chlorine compounds beingreleased may be expelled and advantageously removed in a downstreamoff-gas scrub. The chloride content is advantageously reducible in astationary bed, i.e., for example in the course of calcination in amuffle furnace or on a belt calciner. When a calcination is carried outin a moving bed, for example in a rotary tube, comparatively somewhathigher temperatures can be required to reduce the chloride content thanin a stationary bed, and this can lead to a comparatively furtherreduced BET surface area. Depending on the preferred ratio of chloridecontent and BET surface area, it can therefore be advantageous tooperate selectively with a stationary bed or with a moving bed.

[0013] However, small amounts of water, acids, bases or organiccompounds may be added, provided this does not adversely affect theproperties of the upgraded iron oxide compared to a dry upgradingprocess. Preference is given to calcining commercially available ironoxide without any pretreatment whatever.

[0014] Useful iron oxides for the upgrading according to the inventioninclude all iron oxides, regardless of how obtained. Natural, preferablyindustrially produced and also commercially available iron oxides aresuitable, especially iron oxides generated by working up hydrochloricacid pickling wastes. These iron oxides may contain impurities, forexample a residual chloride content and/or compounds of titanium,manganese, aluminum, chromium, phosphorus, zinc, copper, molybdenum,tungsten, silicon, nickel, magnesium, potassium, sodium, cobalt,vanadium, zirconium, niobium, sulfur, lanthanum, lead, tin and/orcalcium. Of particular suitability are iron oxides which are generatedby spray roasting hydrochloric acid pickling wastes in the steelindustry and are present as Fe₂O₃ having a residual chloride content inthe range from 0 to 10 000 ppm, preferably in the range from 50 to 5000ppm and particularly preferably in the range from 500 to 2000 ppm,usually in the hematite crystal form and in a BET surface area oftypically from 3 to 5 m²/g.

[0015] Iron oxides upgraded according to the invention generally have aresidual chloride content of less than 400 ppm, preferably less than 300ppm and particularly preferably less than 250 ppm, especially less than200 ppm. The average particle size, determined by laser diffraction ashereinbelow described, is generally more than 5 μm, i.e., from 5.1 to200 μm, preferably from 8 to 100 μm, particularly preferably from 10 to80 μm and very particularly preferably from 12 to 30 μm, and the finesfraction having particle sizes of less than 1 μm is generally less than.15% by weight, preferably less than 10% by weight, particularlypreferably less than 5% by weight. The BET surface area of the ironoxides treated according to the invention is generally in the range from0.4 to 5 m²/g, preferably in the range from 0.4 to 3.5 m²/g,particularly preferably in the range from 0.5 to 3 m²/g and especiallyin the range from 0.6 to 2.5 m²/g, very particularly preferably in therange from 0.7 to 2 m²/g. The iron oxides treated according to theinvention generally have a hematite structure. They are useful for awhole series of industrial applications such as pharmaceuticals,cosmetics, magnetic tape coatings, chemical reactions, catalysts or forpreparing catalysts, especially for preparing catalysts fordehydrogenation of ethylbenzene to styrene.

[0016] The industrial production of styrene by dehydrogenation ofethylbenzene can be effected by isothermal processes or by adiabaticprocesses. The isothermal process is generally operated at from 450 to700° C., preferably from 520 to 650° C., in the gas phase with additionof water vapor at from 0.1 to 5 bar, preferably from 0.2 to 2 bar,particularly preferably from 0.3 to 1 bar, especially from 0.4 to 0.9bar. The adiabatic process is generally operated at from 450 to 700° C.,preferably from 520 to 650° C., in the gas phase with addition of watervapor at from 0.1 to 2 bar, preferably from 0.2 to 1 bar, particularlypreferably from 0.3 to 0.9 bar, especially from 0.4 to 0.8 bar.Catalysts for the dehydrogenation of ethylbenzene to styrene can beregenerated by means of water vapor.

[0017] Catalysts for the dehydrogenation of ethylbenzene to styrenegenerally contain iron oxide and an alkali metal compound, for examplepotassium oxide. Such catalysts generally further contain a number ofpromoters. Promoters described include for example compounds of calcium,magnesium, cerium, molybdenum, tungsten, chromium and titanium. Thecatalysts may be prepared using compounds of the promoters that will bepresent in the ready-produced catalyst or compounds which during theproduction process convert into compounds that are present in theready-produced catalyst. The materials used may also include assistantsto improve the processibility, the mechanical strength or the porestructure. Examples of such assistants include potato starch, cellulose,stearic acid, graphite or Portland cement. The materials used can bemixed directly in a mixer, kneader or preferably a muller. They can alsobe slurried up into a sprayable mix and be spray dried to form a powder.Th materials used are preferably processed in a muller or kneader in thepresence of water to form an extrudable mass. The ultrasonic bath (100%setting) was started up and, following a dispersion time of 5 min, themeasurement was carried out under continuing ultrasonication. SpecificBET surface areas were determined according to DIN 66133 and porevolumes and average pore radii according to DIN 66131.

INVENTIVE EXAMPLE 1

[0018] 2 kg of HP type iron oxide from Thyssen-Krupp were heated to 900°C. in a muffle furnace, left in the oven at this temperature for 1 h andsubsequently allowed to cool down with the oven.

INVENTIVE EXAMPLE 2

[0019] Inventive example 1 was repeated at 800° C.

INVENTIVE EXAMPLE 3

[0020] Inventive example 1 was repeated at 850° C.

INVENTIVE EXAMPLE 4

[0021] Inventive example 1 was repeated at 950° C.

INVENTIVE EXAMPLE 5

[0022] 20 g of HP type iron oxide from Thyssen-Krupp were heated to 900°C. in a quartz glass rotary tube under an air stream, maintained thereinat 900° C. for 1 h and then allowed to cool down therein.

INVENTIVE EXAMPLE 6

[0023] Inventive example 5 was repeated, except that the iron oxide wasmaintained at 900° C. for 2 h.

INVENTIVE EXAMPLE 7

[0024] The iron oxide was continuously calcined under an air stream in arotary tube. The rotary tube was equipped with three tappers. The walltemperature of the rotary tube was 970° C. and the residence time of theiron oxide was about one hour.

[0025] The physical properties of the inventively pretreated iron oxidesof inventive examples 1 to 7 are summarized in table 1 and comparedtherein with those of the nonupgraded iron oxide.

INVENTIVE EXAMPLE 8

[0026] A spray slurry prepared by suspending 420 g of potassiumcarbonate (potash), 516 g of cerium carbonate hydrate (40% by weightcerium content), 74 g of ammonium heptamolybdate, 70 g of calciumhydroxide (white chalk hydrate), 55 g of magnesite and 1880 g of theiron oxide upgraded according to inventive example 1 in 4.5 liters ofwater was sprayed to form a powder which was pasted up with sufficientwater (about 500 ml) in the presence of starch in a kneader to form anextrudable mass which was extruded into strands 3 mm in diameter. Thestrands were then dried at 120° C., broken to a length of about 0.8 mmand finally calcined in a rotary tube at 875° C. for 1 h.

INVENTIVE EXAMPLE 9

[0027] 415 ml of a catalyst of inventive example 2 were tested in anexternally heated tubular reactor 3 cm in internal diameter under theconditions reported in table 3.

COMPARATIVE EXAMPLE A

[0028] A catalyst was prepared similarly to inventive example 8 exceptthat the upgraded iron oxide of inventive example 1 was replaced bynonupgraded iron oxide (HP type from Thyssen-Krupp).

COMPARATIVE EXAMPLE B

[0029] 415 ml of the catalyst of comparative example A were testedsimilarly to inventive example 3 in the same reactor under the sameconditions. The results are summarized in table 3. TABLE 1 Properties ofa commercially available iron oxide prepared by the Ruthner process(type HP from Thyssen-Krupp) and of iron oxides prepared therefrom bythe upgrading according to the invention from inventive examples 1 to 7.Fines less BET Residual Average than surface chloride particle size 1 mmarea Iron oxide [ppm] [μm] [% by weight] [m²/g] Untreated HP type 140011 15 4.3 (Thyssen-Krupp) Inventive example 1 66 19 2 1.4 Inventiveexample 2 240 15 2.5 2.1 Inventive example 3 110 18 1.7 1.8 Inventiveexample 4 19 22 1 1.1 Inventive example 5 230 — — 1.6 Inventive example6 190 — — 0.7 Inventive example 7 190 13 1.9 0.9

[0030] TAB. 2 Comparison of physical properties of the catalyst ofinventive example 2, prepared using an iron oxide upgraded according tothe invention, and of the catalyst of comparative example A, preparedaccording to the prior art. BET Average Cut surface area Pore volumepore diameter resistance [m²/g] [ml/g] [μm] [N] Inventive 1.3 0.27 1.2864 example 8 Comparative 2.9 0.25 0.39 51 example A

[0031] TABLE 3 Comparison of conversion and selectivity fordehydrogenation of ethylbenzene to styrene using an inventive catalyst(inventive example 3) and a prior art catalyst (comparative example B).Inventive Comparative Pres- example 9 example B sure Steam/EB Tempera-EB conversion EB conversion LHSV abs. ratio ture (styrene (styrene [h⁻¹][bar] [kg/kg] [° C.] selectivity) selectivity) 0.85 0.5 1.4 590 70.2%(96.2%) 68.3% (96.1%) 0.85 0.5 1.4 570 54.5% (97.2%) 53.9% (97.2%) 0.450.5 1.5 550 46.7% (97.4%) 45.7% (97.2%) 0.45 0.4 1.1 550 46.2% (97.9%)41.5% (97.9%)

1. A process for upgrading an iron oxide, which comprises generatingsaid iron oxide by spray roasting hydrochloric acid pickling wastes fromthe steel industry, and calcining said iron oxide without any otherprocess steps or the addition of other substances at from 840 to 1150°C.
 2. A process as claimed in claim 1, wherein said iron oxide iscalcined at from 850 to 1000° C.
 3. Iron oxide upgraded as claimed inclaim 1 or 2, characterized by a residual chloride content of less than400 ppm.
 4. Iron oxide as claimed in claim 3, characterized by anaverage particle size of more than 5 μm and a particle size fraction ofless than 1 μm of less than 15% by weight.
 5. Iron oxide as claimed inclaim 3, characterized by a chloride content of less than 200 ppm. 6.The use of iron oxide as claimed in claim 3 as a catalyst or forpreparing catalysts.
 7. The use of iron oxide as claimed in claim 3 forpreparing catalysts for dehydrogenating ethylbenzene to styrene.
 8. Acatalyst prepared using an iron oxide as claimed in claims 3 to
 5. 9. Acatalyst as claimed in claim 8, comprising from 20 to 80% by weight ofiron oxide, from 5 to 40% by weight of potassium compound, reckoned aspotassium oxide, and optionally further promoters selected from thecompounds of calcium, magnesium, cerium or molybdenum.
 10. A catalyst asclaimed in claim 8, prepared using an iron oxide comprising an averagepore diameter of more than 0.6 μm.
 11. A catalyst as claimed in claim 8,prepared using an iron oxide having a BET surface area of from 0.4 to 5m²/g.
 12. A catalyst as claimed in claim 8, characterized by a chloridecontent of less than 500 ppm.
 13. A catalyst as set forth in claim 8,characterized by a chloride content of less than 200 ppm.
 14. A processfor dehydrogenating ethylbenzene to give styrene at from 450 to 700° C.and a pressure of from 0.1 to 5 bar, which comprises employing acatalyst as claimed in any of claims 8 to 13.